RELATED ART
The present invention is particularly advantageous in connection with gas-fired heaters having a sealed combustion chamber and a burner having a porous combustion surface that is supplied with a combustible air/fuel mixture by aspiration. The invention is illustrated hereafter with respect to residential hot water heaters.
In such water heaters, the primary air flow exceeds the stoichiometric ratio and no secondary air is required to complete the combustion. This is advantageous since secondary air generally complicates the combustion process, leading to nonuniform combustion areas which are hotter or cooler than the average. Such non-uniformity of combustion leads to localized production of undesirable combustion products, particularly carbon monoxide (CO) and the oxides of nitrogen (NO.sub.x).
In order to reduce the production of NO.sub.x, various types of water heaters have been provided with infrared burners supplied with sufficient primary air to establish complete combustion. Typically, such units employ a powered fan or blower to establish the air/fuel mixture supplied to the infrared burner, or fans or blowers located at the exhaust of the unit to induce flow of the combustion products. U.S. Pat. Nos. 4,492,185 and 4,993,402 illustrate water heater units having infrared burners combined with powered mechanical fans or blowers.
It is also known to provide a water heater utilizing an infrared burner in which combustion is achieved without the use of secondary air and in which powered blowers or fans are not used to induce the flow of the air/fuel mixture or the combustion products. The U.S. Pat. No. 4,510,890 discloses such a unit. In that patent, a water heater is described having a vertically extending, side-mounted infrared burner. A flue stack is connected to the combustion chamber at a location spaced from the upper and lower ends of the combustion chamber. Such flue stack is angulated to the axial center of the tank, and thereafter, extends vertically to its discharge end.
As described in co-pending application Ser. No. 997,889, which is incorporated herein in its entirety, when it is necessary to achieve high burner loading in a relatively small space, maintaining low NO.sub.x emissions becomes even more difficult as increased loading tends to increase the combustion temperature and carbon monoxide and NO.sub.x concentrations in the products of combustion. Substantially sealing the combustion chamber overcomes this tendency by causing a subatmospheric pressure condition in the combustion chamber sufficient to pull excess primary air through the burner to cool the flame and reduce the emissions of carbon monoxide and NO.sub.x to low levels. However, substantially sealing the combustion chamber also exacerbates the tendency of burners operating in combustion chambers to produce a resonance or combustion noise upon ignition of combustion. This resonance can persist for long times and can be unacceptably loud. The tighter the seal, the louder the noise, and the more difficult it becomes to control it.
It is the object of the present invention to overcome the disadvantages of the existing technology, specifically the elimination of low resonance frequency noise observed when the gas-fired heater is initially placed into operation.